Preparation of Mn?Zn ferrite from spent zinc-carbon batteries by alkali leaching,acid leaching and Co-precipitation

The treatment of spent zinc-carbon batteries for the recovery of valuable metals followed by conversion to Mn−Zn ferrite has been conducted employing two-stage alkali and acid leaching and co-precipitation method. In the first stage, leaching process was carried out with 4 M NaOH, which resulted in a recovery of 63.4 %Zn and 0.1% Mn. Electrowinning of alkali leaching solution containing 12.75 g/L Zn at a current density of 0.2 A/cm² produced Zn metal of 15 nm to 30 nm size and 99.9% purity. The second stage leaching of residue with 3 M H₂SO₄ and 6 vol.% H₂O₂ at a solid/liquid ratio of 1∶10 indicated the leaching efficiency of 98.0% Zn, 97.9% Mn and 55.2% Fe. The obtained leaching solution was finally adjusted to suitable mole ratios of Mn∶Zn∶Fe (1∶1∶4) by the addition of Zn and Fe sulfate salts followed by pH control to produce Mn−Zn ferrite powder. The characterization of the ferrite powder showed uniform nano-crystalline particles of about 20 nm size with spinel structure.